1. Field of the Invention
The present invention relates to a torsion beam suspension of an automobile, and particularly relates to an improvement of a torsion beam suspension comprising: a pair of left and right trailing arms which are pivotally supported at their front end portions on a vehicle body, and which support wheels at their rear end portions; a torsion beam which has left and right opposite end portions connected to the trailing arms by welds, and which causes torsion when the trailing arms swing in opposite phases; and gussets which are U-shaped in section and substantially triangular in plane view, and which are connected by welds to inner side surfaces of connecting portions between the trailing arms and the torsion beam.
2. Description of the Related Art
Such a torsion beam suspension is already known as disclosed in Japanese Patent Application Laid-open No. 10-236123.
In the torsion beam suspension, gussets which are U-shaped in section and substantially triangular in plane view are connected by welding to inner side surfaces of connecting portions between trailing arms and a torsion beam, the gussets enhancing torsional rigidity of the connecting portions in order to prevent concentration of stress on the connecting portions between the trailing arms and the torsion beam at the time of torsional deformation of the torsion beam. However, in such a torsion beam suspension, the torsional rigidity abruptly increases in the region of the torsion beam where the inner end portion of the gusset is welded, and torsional stress concentrates thereon.
Thus, in the device disclosed in the above described Japanese Patent Application Laid-open No. 10-236123, the torsion beam is provided with a fragile portion comprising a recess at the portion in front of the gusset tip end portion, thereby alleviating stress concentration on the above described region. However, even if such a fragile portion is provided, torsion rigidity in the inner end portion of the gusset does not change as long as the inner end portion of the gusset is connected to the portion beyond the fragile portion. Therefore, there is rather a fear of significantly reducing the strength of the torsion beam because of cooperation between the stress concentration on the fragile portion and the stress concentration on the inner end portion of the gusset. If the plate thickness of the torsion beam is increased to compensate for the reduction in strength, the weight and cost are disadvantageously increased.